Improved automation of INSTALL file generation.

documentation. Therefore it's now installed by default. If there is no
documentation to be found (i.e., you are not using the distribution)
then this step is skipped.

Add --docdir option to configure to control installation directory.

There's now only one transition value and transition function.
NULL handling in aggregates is a lot cleaner.  Also, use Numeric
accumulators instead of integer accumulators for sum/avg on integer
datatypes --- this avoids overflow at the cost of being a little slower.
Implement VARIANCE() and STDDEV() aggregates in the standard backend.

Also, enable new LIKE selectivity estimators by default.  Unrelated
change, but as long as I had to force initdb anyway...

The .DEFAULT rule in backend/Makefile is harmful -- removed.
Replace `::' rules by `:'.

Fix references to pg_hba.conf(5) since that is no longer a man page.
Make minor repairs to "Compatibility" subsections.

Add information on SET SESSION CHARACTERISTICS.
Fix references to pg_hba.conf(5) since that is no longer a man page.

Rename settings net_server to tcpip_socket, max_backends to max_connections
Add --help and --version to postmaster, reformat help output

* Add option to build with OpenSSL out of the box. Fix thusly exposed
  bit rot. Although it compiles now, getting this to do something
  useful is left as an exercise.

* Fix Kerberos options to defer checking for required libraries until
  all the other libraries are checked for.

* Change default odbcinst.ini and krb5.srvtab path to PREFIX/etc.

* Install work around for Autoconf's install-sh relative path anomaly.
  Get rid of old INSTL_*_OPTS variables, now that we don't need them
  anymore.

* Use `gunzip -c' instead of g?zcat. Reportedly broke on AIX.

* Look for only one of readline.h or readline/readline.h, not both.

* Make check for PS_STRINGS cacheable. Don't test for the header files
  separately.

* Disable fcntl(F_SETLK) test on Linux.

* Substitute the standard GCC warnings set into CFLAGS in configure,
  don't add it on in Makefile.global.

* Sweep through contrib tree to teach makefiles standard semantics.

... and in completely unrelated news:

* Make postmaster.opts arbitrary options-aware. I still think we need to
  save the environment as well.